This resubmitted application requests continued funding for our project to investigate the role of acid ceramidase (AC) in mammalian development and the pathogenesis of Farber disease. During the previous funding period we have: a) shown that AC is essential for mouse development beyond the 2-cell stage, b) demonstrated that AC is a critical component of oocyte development, and can be used to prevent oocyte and embryo apoptosis in vitro, c) revealed a novel, autocatalytic mechanism of AC processing and activation, and identified a new class of AC inhibitors, and d) constructed &#147;floxed&#148;AC conditional knockout mice that also carry a transgene expressing an inducible Cre recombinase (ACcKO/CreTM). In the upcoming funding period we will extend these findings by pursuing the following two aims: 1) Construct &characterize the first viable mouse models of AC deficiency (Farber disease). We will use the ACcKO/CreTM mice to induce the ubiquitous knockout of AC activity during embryogenesis and after birth. We will also breed ACcKO mice to transgenic mice expressing Cre recombinase under the control of cell-specific (macrophage and Purkinje cell) promoters, and use these mice to evaluate the cell-specific functions of AC. The resulting animals and embryos will be characterized pathologically, biochemically, and (for those that survive) clinically. In the event that viable mice are not obtained and/or they do not have a phenotype that is clinically relevant to Farber disease, we will also create &#147;hypomorph&#148;mice using a gene &#147;knock-in&#148;strategy and specific Farber disease mutations. The goal of these studies is to gain further insights into the role of AC in mammalian development, and to provide the first viable models of Farber disease. 2) Further explore the role of AC in oocyte development, and for enhancing the outcome of in vitro fertilization (IVF). Oocytes lacking functional AC will be obtained by inducible or oocyte-specific Cre expression in ACcKO mice, and their in vitro and in vivo survival and maturation will be assessed. We will also continue to optimize conditions to prevent oocyte and embryo apoptosis in vitro using recombinant AC, study the mechanism of AC uptake by oocytes, and evaluate the birth outcomes of embryos treated with AC. The goal of these studies is to gain a more complete understanding of AC&#146;s role in oocyte and early embryo development, and to develop novel approaches for enhancing the outcome of IVF.